1. Field of the Invention
The present invention generally relates to magnetic recording/reproducing apparatus for recording/reproducing signals of high density onto/from the magnetic tape at a high transfer rate by guiding a magnetic tape at high speed and, more particularly, relates to configurations of magnetic heads and magnetic tape wrap angles relative to the magnetic heads.
2. Description of the Related Art
In a field of magnetic recording/reproducing in which signals of high density are recorded/reproduced on/from a magnetic tape guided at high speed, one example of magnetic recording/reproducing apparatus was disclosed in Japanese Patent Publication No. 63-49308, which is effective to maintain a good contact condition between a magnetic tape and a slide face of a magnetic head. What was disclosed in the patent will now be described with reference to FIG. 16.
There is a magnetic gap 100 at the top of a magnetic head 101 in the magnetic recording/reproducing apparatus. A magnetic tape 110 contacts with a magnetic head 101 on a slide face 102 in a sliding manner. In the figure, .alpha.'s represent angles between a direction of a chord joining both ends 104, 105 on slide face 102 and the directions of tangents at ends 104, 105, and .beta..sub.in, .beta..sub.out represent angles between the chordal direction above and the direction of magnetic tape 110 coming in and out of contact with the ends 104, 105 on slide face 102. The angles .beta..sub.in, .beta..sub.out will be hereinafter referred to as "tape wrap angles".
Tape wrap angle .beta..sub.in represents a tape wrap angle with which magnetic tape 110 approaches slide face 102 (the side of end 104) (therefore hereinafter referred to as approaching tape wrap angle), and .beta..sub.out represents a tape wrap angle with which magnetic tape 110 leaves slide face 102 (the side of end 105) (hereinafter referred to as leaving tape wrap angle). Tape wrap angles .beta..sub.in, .beta..sub.out are determined by positions of tape guides 108, 109, for example. Force restricting magnetic tape 110 is generated at both ends 104, 105 of slide face 102 by setting values of .beta..sub.in /.alpha., .beta..sub.out /.alpha. to larger than 1 in the arrangement above.
Magnitudes of restricting force F.sub.in, F.sub.out (where "in", "out" indicate the approaching and leaving sides, respectively) per unit width of magnetic tape 110 controlled as stated above are given by the following equations: EQU F.sub.in = T sin (.beta..sub.in -.alpha.) (1) EQU F.sub.out = T sin (.beta..sub.out -.alpha.) (2)
where T is tape tension per unit width of magnetic tape 110.
Pressing force is generated on slide face 102 by the tape tension T per unit width above, which is given by the following equation: EQU f = T/R (3)
where R is a radius of the curvature of slide face 102.
In this case, when magnetic tape 110 is guided in the direction indicated by the arrow A in the figure, magnetic tape 110 moves in a stable manner under the condition that the restricting forces F.sub.in, F.sub.out and the pressing force f are in harmony with an air film pressure between slide face 102 of magnetic head 101 and magnetic tape 110.
FIG. 17 is a diagram of a spacing distribution when the values of .beta..sub.in /.alpha., .beta..sub.out /.alpha. are 1.2-2.5 as described in Japanese Patent Publication No. 63-49308. The spacing distribution is a distribution of a gap (hereinafter referred to as spacing) between magnetic tape 110 on slide face 102 of magnetic head 101 and slide face 102.
As shown in FIG. 17, the spacing is virtually constant and small over slide face 102. This means that the spacing of magnetic gap 100 on slide face 102 of magnetic head 101 is hardly affected by the moving direction of magnetic tape 110 and disturbance such as vibrations, and a good electromagnetic converting characteristic can be provided at magnetic gap 100.
The effect described above is due to the restricting forces F.sub.in, F.sub.out. Appropriate setting of the values of .beta..sub.in /.alpha., .beta..sub.out /.alpha. is disclosed, for example, in U.S. Pat. No. 4,888,657, U.S. Pat. No. 4,875,129, and Japanese Patent Laying-Open No. 59-16119. According to the references, an air bearing face is formed on the same circumference as that of the slide face having the magnetic gap.
As a representative of the prior art, a magnetic head configuration according to U.S. Pat. No. 4,888,657 is shown in FIG. 18.
In FIG. 18, a magnetic head 101 includes a slide face 102 having a cylindrical shape with a magnetic gap 100. Slots 103a, 103b are formed on slide face 102 at both sides of magnetic gap 100, extending at right angles with the moving direction of magnetic tape 110. Slide face 102 is divided into three raised faces 102a, 102b and 102c by slots 103a and 103b.
In this case, when magnetic tape 110 is guided as far as raised faces 102b and 102c of slide face 102 by tape guides 108 and 109, magnetic tape 110 is restricted by both ends 104, 105 of raised face 102a having the magnetic gap 100 and ends 106, 107 of raised faces 102b, 102c to be air bearing faces. As a result, the magnetic tape wrap angles, .beta..sub.in, .beta..sub.out on raised face 102a are set stably. That is, end 106 of raised face 102b and end 107 of raised face 102c serve as guides, which correspond to tape guides 108, 109 of FIG. 16, respectively.
In the conventional technique (FIGS. 16 and 18), however, even if the values of .beta..sub.in /.alpha., .beta..sub.out /.alpha. are set to 1.2 to 2.5, a good spacing characteristic is not necessarily obtained for some tape tension. Here, the spacing characteristic means a characteristic of a spacing and spacing distribution.
This problem will now be described with reference to FIG. 19.
FIG. 19 is a diagram showing a spacing distribution relative to tape tension when the tape wrap angles are set so that .beta..sub.in / .alpha.= .beta..sub.out /.alpha.= 1.2 to 2.5, and magnetic tape 110 is guided in the direction of the arrow A in FIGS. 16 and 18.
In the figure, the solid line indicates a spacing distribution when the tape tension is optimized. The dot-and-dash line indicates a spacing distribution when the tape tension is rather low. The dotted line indicates a spacing distribution when the tape tension is rather high. That is, when the tape tension is low, magnetic tape 110 flies by a fluid lubrication effect as a restriction effect on magnetic tape 110 on end 104 of slide face 102 of FIG. 16 or raised slide face 102a of FIG. 18 is small. When the tape tension is high, the restricting force of the tape on the both ends 104, 105 of slide face 102 of FIG. 16 or raised face 102a of FIG. 18 is large and stiffness of magnetic tape 110 is increased, so that magnetic tape 110 flies due to deformation of tape 110 at magnetic gap 100.
A second problem in the conventional technique will now be described.
This problem is due to the difference between the approaching tape wrap angle .beta..sub.in and the leaving tape wrap angle .beta..sub.out in FIGS. 16 and 18.
FIG. 20 is a diagram showing a change of a spacing distribution with the leaving tape wrap angle .beta..sub.out being constant while the approaching tape wrap angle .beta..sub.in being changed. In this case, the values of .beta..sub.in /.alpha., .beta..sub.out /.alpha. are in the range of 1.2 to 2.5. The spacing distribution in this case varies with tape tension. In the figure, the solid line, the dot-and-dash line, and the dotted line indicate spacing distributions when .beta..sub.in = .beta..sub.out, .beta..sub.in &lt;&lt; .beta..sub.out, and .beta..sub.in &gt;&gt; .beta..sub.out, respectively. That is, for some tape tensions set, when there is a large difference between the approaching tape wrap angle .beta..sub.in and the leaving tape wrap angle .beta..sub.out, a good contact condition cannot be created between magnetic tape 110 and slide face 102 of magnetic head 101 (FIG. 16), or magnetic tape 110 and raised slide face 102a of magnetic head 101 (FIG. 18).
A third problem in the conventional technique will now be described.
This problem is related to a distance between guides for setting the tape wrap angles .beta..sub.in, .beta..sub.out . A spacing characteristic changes depending on distance between guides. For example, a spacing characteristic with a relatively long distance between the guides, such as, the distance between tape guides 108, 109 shown in FIG. 16 is different from that with a short distance, such as, the distance between end 106 of raised face 102b and end 107 of raised face 102c in FIG. 18.
FIG. 21 is a diagram for describing the problem above.
In this case, the tape tension and the tape wrap angles are so set that a good spacing characteristic is obtained with a short distance between the guides. In the figure, the solid line and the dot-and-dash line indicate spacing distributions with a short distance and a long distance between the guides, respectively.
As shown in the figure, since the spacing characteristic varies with the distance between the guides, the tape tension and the tape wrap angles must be set appropriately according to the distance in order to obtain a good spacing characteristic.
As described above, the first, second and third problems indicate that the spacing characteristic is determined by a correlation between the guide distance, the approaching tape wrap-angle .beta..sub.in, and the leaving tape wrap angle .beta..sub.out and if these parameters are set inappropriately, a good spacing characteristic cannot be obtained. In this case, magnetic gap 100 of magnetic head 101 cannot display a full electromagnetic converting characteristic. This becomes more significant with shorter recording wavelength on magnetic tape 110.